Fluid-flow machines, of which, in the heat-engine category, the gas turbine constitutes a widespread energy-converting unit, are used for the generation of energy. Gas turbines are operated with liquid and/or gaseous fuels. A typical recuperator gas-turbine construction has an air compressor, also called turbocompressor, which draws in fresh air, which is typically compressed to a pressure of 4 to 8 bar and, in certain circuits, is forced into a heat exchanger, in which it is preferably preheated by still hot combustion gases flowing from the turbine. In plants without a recuperator, the pressure at the end of the compressor is typically 12-30 bar. Finally, the preheated and compressed supply air passes together with fuels into a combustion chamber, in the course of which hot or combustion gases higher than 1200.degree. C. are produced. These combustion gases flow at high velocity into the turbine and drive the latter, which is normally coupled to a generator for the generation of electricity.
A multiplicity of efforts are made to improve the operation of gas turbines with regard to their power density and their efficiency. The efficiency of a gas turbine depends in principle on the ratio of the energy input into gas turbine to the energy converted by the gas turbine, which energy can be converted into electrical energy by means of a generator. It is thus necessary to reduce the proportion of energy which is theoretically made available to the gas turbine by the combustion gases but is not converted into electrical energy.
A large proportion of the losses of a gas turbine is connected with the relatively high temperatures at the turbine outlet. So that as high a percentage as possible of the heat supplied in the combustion chamber can be converted into mechanical power by the turbine, the pressure ratio of the gas turbine must be selected to be as high as possible.
However, high pressure ratios have the disadvantage that the compressed air is very hot. The result of this is that, at a fixed turbine outlet temperature, with increasing pressure ratio, an ever decreasing amount of heat per kilogram of air can be directed into the combustion chamber. In addition, it is no longer possible to preheat the air, since the air temperature downstream of the compressor, at a high pressure ratio, becomes higher than the exhaust-gas temperature downstream of the turbine.
A further important source of losses in gas turbines is connected with the fact that about 2/3 of the mechanical power of the turbine has to be applied for driving the compressor. Since the turbine and compressor have component efficiencies which are less than 1, the power output of the turbine to the compressor leads to a product efficiency which corresponds to the product of the component efficiencies and is therefore markedly lower than the component efficiencies.
The abovementioned reasons lead to a compromise. The maximum power density of a gas turbine is achieved at a lower pressure ratio than the maximum efficiency. As a rule, the pressure ratio of the gas turbine is therefore selected such that an optimum compromise between power and efficiency is achieved. In addition to the improvement of the abovementioned aspects with regard to the power density and the efficiency of gas turbines, the thermal loading capacity of the individual components which are necessary for the operation of gas turbines is also increasingly important for the conception and design of such plants. Not least for reasons of competition, it is necessary to design gas-turbine plants in such a way that they are not too complicated and consequently not too costly, but on the other hand it is necessary to offer durable and high-quality products.
Thus, for example, conventional compressor stages in each case consist of a rotor and a stator, which are fitted with moving and guide blades and by means of which the air flowing through the compressor stage is heated by the compression from ambient temperature up to above 500.degree. C. Such high temperatures put a considerable strain on the materials used in the compressor stage, and this has a lasting harmful effect on the service life of the individual components involved, so that complicated and extensive cooling measures have to be taken in order to increase the resistance of the materials in the compressor region to the high temperatures which occur. In addition, since the cooling air is very hot, the cooling is difficult and uses a great deal of cooling air.